Time adjustment device, timekeeping device with a time adjustment device, and a time adjustment method

ABSTRACT

A time adjustment device having a time information generating unit that generates and outputs time information containing internal time data; a reception unit that receives satellite signals transmitted from a positioning information satellite in subframe information units; an external input unit that generates, through manual operation thereof, command information that instructs the reception unit to enter a reception mode; a reception timing start setup unit that, when in the reception mode, sets the start time of reception so that the subframe information units are acquired at the time determined by the internal time data; and a corrected time information storage unit that stores the satellite-time-related information as corrected time information. A determination unit determines whether the satellite-time-related information received in a particular segment of subframe information unit(s) is correct or erroneous, and if correct, is used as time adjustment information to correct the generated time information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims priority under 35U.S.C. §120 on, U.S. application Ser. No. 12/176,037, filed Jul. 18,2008, which claims priority under 35 U.S.C. §119 on Japanese patentapplication nos. 2007-202085 and 2008-108618, filed Aug. 2, 2007 andApr. 18, 2008 respectively. Each of these prior applications is herebyincorporated by reference in its entirety.

BACKGROUND

1. Field of Invention

The present invention relates to a time adjustment device that correctsthe time based on signals from a positioning information satellite suchas a GPS satellite, to a timekeeping device that has the time adjustmentdevice, and to a time adjustment method.

2. Description of Related Art

The Global Positioning System (GPS) for determining the position of aGPS receiver uses GPS satellites that circle the Earth on known orbits,and each GPS satellite has an atomic clock on board. Each GPS satellitetherefore keeps the time (referred to below as the GPS time) withextremely high precision.

Japanese Unexamined Patent Appl. Pub. JP-A-H11-211858 teaches aradio-controlled timepiece that analyzes the time code contained in along-wave standard time signal to correct the displayed time instead ofusing GPS satellite signals or a method of correcting the time based onGPS time information.

The time information transmitted in a GPS satellite signal is updated ona predetermined cycle. Japanese Unexamined Patent Appl. Pub.JP-A-H11-125666 teaches technology for predicting the GPS timeinformation after being updated at this predetermined period, predictingthe time of the next GPS time signal, and using this predicted time toacquire the positioning information for the device location. Measuringthe pseudo range to the GPS satellite and determining the currentposition is therefore possible even when the reception environment isnot ideal.

Japanese Unexamined Patent Appl. Pub. JP-A-H10-82875 teaches a method ofcorrecting the time using the time information (GPS time) from a GPSsatellite.

This method acquires the navigation message at full power (that is, withthe CPU running and other parts operating) immediately after the poweris turned on. The time information contained in the acquired navigationmessage is then acquired and the time is calculated. The time is thencalculated and the timing for the next correction is determined from therelationship between the precision of the crystal that generates thereference clock signal of the device and the required precision of thetimepiece. More specifically, the time when the next navigation messagewill be acquired (when the CPU is stopped and a sleep mode is active) isdetermined. The navigation message is then acquired again after thesleep mode ends, and the time is corrected based on the time informationacquired from the navigation message.

With this method the receiving device determines when to receive the GPSsignal, such as immediately after the power turns on. The user, however,might also want to force adjusting the time based on the received GPStime. In such cases the reception time must be adjusted so that the GPStime can be received and the time can be adjusted at a time close towhen the user wants to adjust the time. However, because minimizingpower consumption is essential in a timepiece or other small device, itis also essential to acquire the information needed to set the time inthe shortest time possible even when satellite signals are received froma GPS satellite or other positioning information satellite to adjust thetime at a timing close to when the user wants to adjust the time.

SUMMARY OF INVENTION

A time adjustment device, a timekeeping device with the time adjustmentdevice, and a time adjustment method according to preferred aspects ofthe present invention receive time data efficiently in a short time andenable correcting the time without greatly increasing the powerconsumption at a timing close to when the user wants to adjust the time.

A first aspect of the invention is a time adjustment device comprising atime information generating unit that generates time informationcontaining internal time data and that outputs the generated timeinformation; a reception unit that receives satellite signalstransmitted sequentially from a positioning information satellite insubframe information units that comprise subframes 1 to 5 and thatcontain satellite-time-related information; an external input unit thatgenerates, through manual operation of an external operating unit,command information that instructs the reception unit to enter areception mode; a reception timing start setup unit that, when in thereception mode, sets the start time of reception by the reception unitso that the subframe information units are acquired at the timedetermined by the internal time data; and a corrected time informationstorage unit that stores the satellite-time-related information ascorrected time information; wherein the reception unit comprises adetermination unit that determines whether the satellite-time-relatedinformation received in a particular segment of one or more subframeinformation units is correct or erroneous, and if correct, is used astime adjustment information, and wherein the generated time informationis corrected based on the time adjustment information reception.

In this aspect of the invention the external input unit is used togenerate command information instructing the reception unit to enter areception mode. The reception timing start set up unit sets the starttime of reception by the reception unit so that the subframe informationunits are acquired at the time determined by the internal time data. Thesatellite-time-related information in the satellite signal received bythe reception unit is stored in the corrected time information storageunit as corrected time information. The generated time information isthen corrected based on the time adjustment information.

The generated time information is thus corrected based on the timeadjustment information that is received when reception is initiated byinput from the user, for example. The time adjustment device cantherefore correct the generated time information at a timing close tothe time when the user wants to set the time. Furthermore, because thetime adjustment device starts reception in response to user input, powerconsumption can be reduced compared with when the time signal isreceived automatically at a regular interval.

A determination unit is provided that determines if the receivedsatellite-time-related information is correct, and thus whether to useit as time adjustment information or not. By correcting the time basedon satellite-time-related information that is determined to be correctand thus reliable, the time can be corrected accurately.

Preferably, the positioning information satellite is a GPS satellite.

In another aspect of the invention, a week number is contained insubframe 1, and the reception unit receives the week number.

In a time adjustment device according to another aspect of theinvention, if a current corrected amount of time, which the amount oftime the generated time information was corrected based on the timeadjustment information, exceeds a prescribed threshold amount, then thesatellite-time-related information received in a subsequent subframeinformation unit is stored, and if consistent, the generated timeinformation is corrected based on the selected satellite data.

In a time adjustment device according to still another aspect of theinvention, if a current corrected amount of time, which the amount oftime the generated time information was corrected based on the timeadjustment information, exceeds a prescribed threshold amount, then thesatellite-time-related information received in each of a plurality ofsubsequent subframe information units is stored by unit as satellitetime data, and one out of at least two of the satellite time data inwhich the difference approximately matches the difference between thecorresponding subframe information units is selected. Then, thegenerated time information is corrected based on the selected satellitedata.

In this way, the time adjustment device thus avoids using inaccuratetime adjustment information to correct the generated time information,and can therefore suppress further deviation in the corrected generatedtime information.

Other objects and attainments together with a fuller understanding ofthe invention will become apparent and appreciated in light of thefollowing description and claims taking in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a GPS wristwatch according to afirst embodiment of the invention.

FIG. 2 is a section view of the GPS wristwatch shown in FIG. 1.

FIG. 3 is a block diagram showing the main internal hardwareconfiguration of the GPS wristwatch according to the first embodiment ofthe invention.

FIG. 4 is a schematic diagram showing the main software configuration ofthe GPS wristwatch according to the first embodiment of the invention.

FIG. 5 shows data stored in the program storage unit shown in FIG. 4.

FIG. 6 shows data stored in the first data storage unit shown in FIG. 4.

FIG. 7 shows data stored in the second data storage unit shown in FIG.4.

FIG. 8 is a flow chart showing the main steps in the operation of theGPS wristwatch according to the first embodiment of the invention.

FIG. 9 is a flow chart showing the main steps in the operation of theGPS wristwatch according to the first embodiment of the invention.

FIGS. 10A and 10B show the structure of the navigation message.

FIG. 11 shows the structure of word data in a subframe 1.

FIGS. 12A and 12B show the time sequence of the navigation messagereception period of the GPS wristwatch according to the first embodimentof the invention.

FIG. 13 shows data stored in the program storage unit of a GPSwristwatch according to a second embodiment of the invention.

FIG. 14 shows data stored in the second data storage unit of a GPSwristwatch according to a second embodiment of the invention.

FIG. 15 is a flow chart showing the main steps in the operation of theGPS wristwatch according to the second embodiment of the invention.

FIG. 16 is a flow chart showing the main steps in the operation of theGPS wristwatch according to the second embodiment of the invention.

FIG. 17 shows the time sequence of the navigation message receptionperiod of the GPS wristwatch according to the second embodiment of theinvention.

FIG. 18 is a flow chart showing the main steps in the operation of theGPS wristwatch according to a third embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of a time adjustment device, a timekeeping devicewith a time adjustment device, and a time adjustment method according tothe present invention are described below with reference to theaccompanying figures.

Embodiment 1

FIG. 1 is a schematic diagram showing a wristwatch with a GPS timeadjustment device 10 (referred to below as a GPS wristwatch 10) as anexample of a timekeeping device with a time adjustment device accordingto a first embodiment of the present invention. FIG. 2 is a section viewof the GPS wristwatch 10 shown in FIG. 1. FIG. 3 is a block diagramshowing the main internal hardware configuration of the GPS wristwatch10 shown in FIG. 1 and FIG. 2.

As shown in FIG. 1 and FIG. 2, the GPS wristwatch 10 has a time displayunit and a display 14 on the front. The time display unit includes adial 12 and hands 13 such as the second hand, minute hand, and hourhand. The display 14 in this aspect of the invention is an LCD panelused for presenting location information such as the latitude andlongitude or the city name, as well as other informational messages. Thehands 13 are driven through a wheel train by means of a stepping motorthat includes a motor coil 19.

As shown in FIG. 1, the GPS wristwatch 10 also has an external operatingunit 5 for externally inputting reception commands, for example, to theGPS wristwatch 10. More particularly, in this embodiment of theinvention the user can use the external operating unit 5 to enter acommand to receive time signals from a GPS satellite 15 a (or satellites15 b to 15 d) and adjust the time.

As shown in FIG. 2, the GPS wristwatch 10 has a GPS antenna 11. The GPSantenna 11 is a part of the receiver device 40 (see FIG. 3). This GPSantenna 11 is a patch antenna for receiving satellite signals from aplurality of GPS satellites 15 a to 15 d orbiting the Earth on fixedorbits in space. This GPS antenna 11 is located on the opposite side ofthe dial 12 as the side on which the time is displayed. The dial 12 ismade of plastic or other material that passes RF signals such as thesignals transmitted from the GPS satellites 15 a to 15 d.

The GPS satellites 15 a to 15 d are an example of a positioninginformation satellite, and a plurality of GPS satellites 15 a to 15 dorbit the Earth in space. In this embodiment of the invention satellitesignals are received from the GPS satellite 15 a (or 15 d to 15 d)located where signals can currently be most easily received. Note thatfour GPS satellites 15 a to 15 d are shown in FIG. 1 by way of example,and the number of GPS satellites is not so limited.

The outside case 17 is made of stainless steel, titanium, or othermetal. The bezel 16 is preferably ceramic in order to improve thereception performance of the GPS antenna 11 that receives satellitesignals from the GPS satellites 15 a (15 b to 15 d). The crystal 18(front glass unit) is fit into the bezel 16.

The battery 24 is a lithium-ion battery or other type of storagebattery. A magnetic sheet 21 is disposed below the battery 24, and acharging coil 22 is disposed with the magnetic sheet 21 between it andthe battery 24. The battery 24 can therefore be charged by the chargingcoil 22 by means of electromagnetic induction from an external charger.

The magnetic sheet 21 can also divert the magnetic field. The magneticsheet 21 therefore reduces the effect of the battery 24 and enables theefficient transmission of energy. A back glass unit 23 is also disposedin the center part of the back cover 26 to facilitate powertransmission.

The GPS wristwatch 10 is arranged as described above.

As shown in FIG. 3, the GPS wristwatch 10 also has a time display device45, a receiver device 40, and a time adjustment device 44, and functionsas a computer. The configuration shown in FIG. 3 is further describedbelow.

As shown in FIG. 3, the GPS wristwatch 10 has a receiver device 40 andpasses satellite signals received from a GPS satellite 15 a (15 b to 15d) in FIG. 1 from the GPS antenna 11 through a filter (SAW) 31 and RF(radio frequency) unit 27 to extract the signal by means of the basebandunit 30.

More specifically, the filter (SAW) 31 is a bandpass filter and in thisembodiment of the invention extracts a 1.5-GHz satellite signal. Theextracted satellite signal is amplified by an LNA 47, mixed by a mixer46 with a signal supplied from a VCO 41, and down-converted to an IF(intermediate frequency) signal. The clock signal for the PLL 34 isgenerated by a temperature-compensated crystal oscillator (TCXO) 32.

The satellite signal passes the IF filter 35 and IF amplifier, and isconverted to a digital signal by the A/D converter 42. The baseband unit30 then processes the satellite signal based on a control signal. Thetime data output by the baseband unit 30 is stored in a storage unit,and the corrected time information is displayed by means of a drivecircuit 43.

The receiver device 40 includes an RF unit 27 and baseband unit 30. TheRF unit 27 includes a PLL 34, IF filter 35, VCO 41, A/D converter 42 andLNA 47.

The receiver device 40 that includes the GPS antenna 11 and filter (SAW)31 is an example of a reception unit, and is also referred to an a GPSdevice. The receiver device 40 including the GPS antenna 11 and filter(SAW) 31 is referred to below as simply the receiver device 40.

The baseband unit 30 also includes a digital signal processor (DSP) 39,a CPU (central processing unit) 36, and SRAM (static random accessmemory) 37, and is connected to the temperature-compensated crystaloscillator (TCXO) 32 and flash memory 33.

A real-time clock (RTC) 38 is disposed to the control unit 20. Thereal-time clock 38 counts up at a reference clock that is determined bya crystal oscillator connected to the control unit 20. The control unit20 includes a CPU 20 a.

The charging coil 22 charges the battery 24, which is a storage battery,with power through a charging control circuit 28, and supplies drivepower from the battery 24 to the time adjustment device 44 and otherparts through a regulator 29. The control unit 20 also outputs a controlsignal to the receiver device 40.

The GPS wristwatch 10 controls the reception operation of the receiverdevice 40 by means of the control unit 20.

The GPS wristwatch 10 according to this embodiment of the invention isthus an electronic timepiece. The real-time clock 38 is an example of atime information generating unit for generating time information. Theinternal time data 73 b (see FIG. 7) that is the time informationgenerated by the real-time clock 38 is an example of generated timeinformation. The receiver device 40 is an example of a reception unit.

FIG. 4 to FIG. 7 schematically describe the main software structure ofthe GPS wristwatch 10, FIG. 4 being an overview.

As shown in FIG. 4, the control unit 20 of the GPS wristwatch 10 runsprograms stored in the program storage unit 50 in FIG. 4, and processesdata stored in the first data storage unit 60 and data stored in thesecond data storage unit 70.

FIG. 5 shows the data stored in the program storage unit 50 in FIG. 4.FIG. 6 shows the data stored in the first data storage unit 60 in FIG.4. FIG. 7 shows the data stored in the second data storage unit 70 inFIG. 4.

The first data storage unit 60 in FIG. 6 stores primarily previouslystored data, and the second data storage unit 70 in FIG. 7 storesprimarily data resulting from processing the data in the first datastorage unit 60 by means of a program stored in the program storage unit50.

FIG. 8 and FIG. 9 are flow charts describing the main steps in theoperation of the GPS wristwatch 10 according to this embodiment of theinvention.

The programs and data shown in FIG. 5 to FIG. 7 are described belowwhile describing the operation of the GPS wristwatch 10 according tothis embodiment of the invention with reference to the flow charts inFIG. 8 and FIG. 9.

First, as shown in FIG. 7, whether the external operating unit 5 (anexample of an external input unit) was operated and a reception commandwas asserted is determined in step ST10. More specifically, if the userwants to receive the satellite signal from the GPS satellites 15 a (15 bto 15 d) to adjust the time displayed by the hands 13, for example, theuser operates the external operating unit 5 and inputs a command toreceive a GPS satellite 15 a (15 b to 15 d) signal.

The reception command input from the external operating unit 5 is storedas the reception instruction data 75 a in the reception instruction datastorage unit 75 shown in FIG. 7. The operating signal confirmationprogram 54 in FIG. 5 checks the reception instruction data storage unit75 in FIG. 7 and determines if the reception instruction data 75 a isstored.

If it is confirmed in step ST10 that the reception instruction data 75 ais stored in the reception instruction data storage unit 75 in FIG. 7,control goes to step ST11.

The timing for starting to receive signals from a GPS satellite 15 a (15b to 15 d) is set in step ST11 based on the reception instruction data75 a, and is stored as the time-to-start-reception data. Morespecifically, the start-reception data configuration program 58 in FIG.5 (an example of a start-reception data configuration unit) confirms thetime that the reception instruction data 75 a in FIG. 7 was stored basedon the internal time data 73 b in FIG. 7. The start-reception dataconfiguration program 58 then generates the start reception data 76 abased on the reception timing data 61 a stored in the reception timingdata storage unit 61 in FIG. 6.

The start-reception data configuration program 58 in FIG. 5 generatesand stores the start reception data 76 a in the start reception datastorage unit 76 so that the internal time data 73 b in FIG. 7 iscorrected at the 0 second or 30 second of the minute closest to the timeof the reception instruction data 75 a.

More specifically, if the time when the user operates the externaloperating unit 5 to input the GPS satellite 15 a (15 b to 15 d) signalreception command and the reception instruction data 75 a is stored isbetween 07:00:21 and 07:00:49, a time between 07:00:50 to 07:00:58 isstored as the start reception data 76 a depending on the GPS satellite15 a (15 b to 15 d) search time. Signal reception is then set to startwhen the internal time data 73 b goes to 07:01:00.

If the time of the reception instruction data 75 a is between 07:00:51and 07:01:19, a time between 07:01:20 to 07:01:28 is stored as the startreception data 76 a. Signal reception is then set to start when theinternal time data 73 b goes to 07:01:30.

The reception instruction data 75 a is thus set so that the internaltime data 73 b is corrected at a predetermined time at the 0 second or30 second of the minute.

The start reception data 76 a is thus set to a time before transmissionof subframe 1 (an example of a subframe information unit) of the GPSsatellite 15 a (15 b to 15 d) signal starts as further described below.

In addition to the GPS satellite 15 a (15 b to 15 d) search time, thestart reception data 76 a is also set with consideration for the startuptime of the RF unit 27 of the receiver device 40. As a result, the startreception data 76 a is set to start searching for a GPS satellite 15 a(15 b to 15 d) approximately 2-10 seconds before transmission ofsubframe 1 starts.

Control then goes to step ST12. In step ST12 the internal time data 73 bin FIG. 7 is referenced to determine if it is the time indicated by thestart reception data 76 a. More specifically, the reception timingdetermination program 51 in FIG. 5 reads and determines if the internaltime data 73 b in FIG. 7 equals the start reception data 76 a in FIG. 7.For example, because the start reception data 76 a in this example is atime from 07:01:20-07:01:28, whether the time denoted by the internaltime data 73 b has reached 07:01:20-07:01:28 is confirmed.

If the time denoted by the internal time data 73 b does not equal thestart reception data 76 a, the start of reception waits until the timebased on the internal time data 73 b reaches the start reception data 76a.

When time based on the internal time data 73 b reaches the startreception data 76 a, control goes to step ST13. Receiving signals fromthe GPS satellite 15 a (15 b to 15 d) then starts in step ST13. Thereceiver device 40 therefore starts to prepare for searching for a GPSsatellite 15 a (15 b to 15 d).

More specifically, the receiver device 40 starts operating and generatesthe C/A code pattern for a particular GPS satellite 15 a (15 b to 15 d)in order to receive the satellite signal through the GPS antenna 11.

Control then goes to step ST14 and the GPS satellite search starts. Moreparticularly, the satellite search program 52 in FIG. 5 causes thereceiver device 40 to adjust the output timing of the C/A code patternfor a particular GPS satellite 15 a (15 b to 15 d) and searches for aGPS satellite 15 a (15 b to 15 d) signal with which the receiver device40 can synchronize.

Note that the amount of time needed to locate a GPS satellite 15 a (15 bto 15 d) depends partly upon whether or not orbit information for theGPS satellites 15 a to 15 d is stored locally. Searching requiresseveral seconds if operating from a cold start with no locally storedorbit information.

The GPS wristwatch 10 determines the time when the satellite searchstarts according to whether or not there is locally stored orbitinformation so that the subframe 1 data can be reliably received.

Proceeding to step ST15, the receiver device 40 adjusts the timing atwhich the receiver device 40 generates the C/A code of the GPS satellite15 a (15 b to 15 d), and determines if the time until synchronization ispossible is greater than or equal to a prescribed time.

More specifically, the stop reception determination program 57 in FIG. 5counts the time from the start of reception, and determines if the timerequired to find a GPS satellite 15 a (15 b to 15 d) exceeds apredetermined time. If this predetermined time or longer has passed,operation times out, control goes to step ST16, and reception ends.

As a result, if the GPS wristwatch 10 is located where the GPS satellite15 a (15 b to 15 d) signal cannot be received, such as indoors, and thereceiver device 40 is driven for a long time in order locate asatellite, a large amount of power will be consumed. The GPS wristwatch10 according to this embodiment of the invention therefore terminatesreception when a predetermined time has passed in order to avoidneedlessly consuming power.

If operation has not timed out in step ST15, control goes to step ST17.

Step ST17 determines if a GPS satellite 15 a (15 b to 15 d) wascaptured. More specifically, the satellite search program 52 in FIG. 5causes the receiver device 40 to search for and synchronize with a GPSsatellite 15 a (15 b to 15 d). The satellite search program 52 thendetermines of the navigation message that is an example of a satellitesignal from the GPS satellite 15 a (15 b to 15 d) as described below canbe decoded.

If a GPS satellite 15 a (15 b to 15 d) cannot be captured, the procedureloops to step ST14 and the GPS satellite 15 a (15 b to 15 d) searchrepeats to find a different GPS satellite 15 a (15 b to 15 d).

If a GPS satellite 15 a (15 b to 15 d) is captured, control goes to stepST18 in FIG. 9 to acquire the navigation message from the satellitesignal.

Before proceeding to step ST18, the navigation message carried by thesignal (satellite signal) transmitted from the GPS satellite 15 a (15 bto 15 d) is described below.

FIG. 10 schematically describes the navigation message.

As shown in FIG. 10A, signals are transmitted from each of the GPSsatellite 15 a (15 b to 15 d) in units of one frame every 30 seconds.One frame contains five subframes (subframe 1 to subframe 5). Eachsubframe is 6 seconds long, and contains 10 words (each word is 0.6second).

The first word in each subframe is a telemetry (TLM) word storing theTLM data, and each TLM word starts with a preamble as shown in FIG. 10B.

The TLM word is followed by a handover word HOW storing the HOW(handover) data, and each HOW starts with the time of week (TOW) (alsocalled the Z count) indicating the GPS time information of the GPSsatellite.

The GPS time is the number of seconds since 00:00:00 Sunday night, andis reset to zero at precisely 00:00:00 every Sunday night. The GPS timeis thus information expressing the time since the start of the week inseconds, and the elapsed time is a number expressed in 1.5 second units.The GPS time is also called the Z count (referred to below as the Zcount data), is an example of satellite-time-related information, andenables the receiver device 40 to know the current time.

The same GPS week number is added to the GPS time throughout the week,and is contained as the week number data in the navigation message orsatellite signal from the GPS satellite.

The starting point for the GPS time information is 00:00:00 of Jan. 6,1980 referenced to the Coordinated Universal Time (UTC), and the weekthat started on that day is week 0. The GPS receiver can therefore getthe precise GPS time from the week number and the elapsed time (numberof seconds) (Z count data).

The week number is updated once a week.

Therefore, if the receiver device 40 has already acquired the weeknumber and has counted the time passed since the week number data wasacquired, the current week number of the GPS satellite 15 a (15 b to 15d) can be known from the acquired week number and the Z count datawithout acquiring the week number data again. By therefore normallyacquiring only the Z count data, the reception operation of the GPSwristwatch 10 can be completed in a short time and power consumption canbe reduced.

As shown in FIG. 10B, the subframe ID data, which is the subframenumber, is contained in the word following the Z count data in the HOWword. The subframe ID data enables the GPS wristwatch 10 to know fromwhich of subframes 1 to 5 the received subframe data was read.

As shown in FIG. 10, the main frame of the navigation message containedin the signal from the GPS satellite 15 contains 1500 bits and istransmitted at 50 bps.

The main frame is divided into five subframes of 300 bits each (see FIG.10A). Subframe 1 to subframe 5 therefore contain the TLM word and the Zcount (TOW) data in the HOW word.

In addition to the TLM word and HOW, the navigation message alsoincludes the ephemeris (detailed orbit information for the transmittingGPS satellite 15 a (15 b to 15 d)), almanac (orbit information for allGPS satellites 15 a to 15 d), and the UTC data (universal time,coordinated) not shown.

FIG. 11 schematically describes part of the word data (WORD 1 to WORD 5)in subframe 1.

As shown in FIG. 11, word 3 in subframe 1 contains the week number (WN)data and satellite health (SVhealth) data, which is a signal describingthe operating condition of the GPS satellite 15 a (15 b to 15 d).

Because the navigation messages from the GPS satellites 15 a to 15 d aretransmitted as described above, receiving signals from the GPS satellite15 a (15 b to 15 d) in this embodiment of the invention means phasesynchronization with the C/A code from the GPS satellite 15 a (15 b to15 d) affording the best reception conditions from among all of the GPSsatellites 15 a to 15 d.

The C/A code (a 1023-chip pseudo random noise code that repeats every 1ms) is used for synchronizing with 1 ms precision. The C/A code (1023chip (1 ms) code) is different for each of the GPS satellites 15 a (15 bto 15 d) orbiting the Earth, and is unique to a particular satellite.

Therefore, to receive the satellite signal from a particular GPSsatellite 15 a (15 b to 15 d), the receiver device 40 (reception unit)generates and phase synchronizes with the unique C/A code for theparticular GPS satellite 15 a (15 b to 15 d) in order to receive thesatellite signal.

By synchronizing with the C/A code (1023 chips (1 ms)), the navigationmessage can be received, and the preamble of the TLM word and the HOWword of each subframe can be received, and the Z count data can beacquired from the HOW word. After acquiring the TLM word and the Z count(TOW) from the HOW word, the receiver device 40 can then acquire theweek number (WN) data and the satellite health data SVhealth.

The satellite health data SVhealth enables determining the operatingcondition of the GPS satellite 15 a (15 b to 15 d) being received aswell as the other GPS satellites 15 a (15 b to 15 d). Whether someproblem has developed with the GPS satellite 15 or whether the satelliteis a test satellite can be determined from this satellite health dataSVhealth.

Whether the acquired Z count data can be trusted can be determined witha parity check. More specifically, the parity data following the Z countdata of the HOW word can be used to verify if the received data iscorrect. If an error is detected by the parity check, there is somethingwrong with the Z count data and the Z count data is not used to correctthe internal clock.

Returning to FIG. 9, if a satellite was captured in step ST17, controlgoes to step ST18. Step ST18 determines if the Z count data wasacquired.

More specifically, the time data acquisition program 53 in FIG. 5receives the navigation message from the GPS satellite 15 a (15 b to 15d) and acquires the Z count data. The Z count (TOW) data is then storedas the received satellite time information 71 a in the receivedsatellite time information storage unit 71 in FIG. 7.

The time information matching program 501 in FIG. 5 (an example of adecision unit) then determines if the received satellite timeinformation 71 a in FIG. 7 (an example of satellite-time-relatedinformation), that is, the acquired Z count data, can be trusted.

More specifically, the time information matching program 501 in FIG. 5verifies whether the received data is correct based on the parity datafollowing the Z count data in the HOW word. If an error is detected bythe parity check, there is some sort of problem with the acquired Zcount data and the Z count data is therefore not used to correct theinternal clock.

As a result, if an error is detected the time data acquisition program53 in FIG. 5 determines that the Z count data was not acquired andcontrol goes to step ST14 in FIG. 8.

However, if in step ST18 the time information matching program 501 inFIG. 5 does not detect an error, the time data acquisition program 53 inFIG. 5 determines that the acquired Z count data can be used to correctthe time, and stores the received satellite time information 71 a in thereceived satellite time information storage unit 71 as the firstreception time data 73 a 1 (an example of correction time information)of the reception time data 73 a (an example of correction timeinformation) in the time data storage unit 73 (an example of acorrection time information storage unit). The Z count data is thusdetermined to have been acquired and control goes to step ST19.

Step ST19 then acquires the satellite health data SVhealth describedabove.

More specifically, the other satellite information acquisition program55 in FIG. 5 gets the satellite health data SVhealth contained in word 3of subframe 1. The other satellite information acquisition program 55 inFIG. 5 then stores the acquired satellite health data as the satellitehealth information 72 a (an example of satellite health information) inthe satellite health information storage unit 72 in FIG. 7.

Control then goes to step ST20 to determine if the satellite healthinformation 72 a in FIG. 7 indicates that the GPS satellite 15 a (15 bto 15 d) is functioning correctly. More specifically, the satellitehealth confirmation program 56 (an example of a condition evaluationunit) evaluates the operating condition of the GPS satellite 15 a (15 bto 15 d) based on the satellite health information 72 a.

If the satellite health information 72 a is a code value other than 0,the satellite health information 72 a indicates some problem and thereceiver knows that the GPS satellite 15 a (15 b to 15 d) cannot beused. If the satellite is healthy, the satellite health information 72 ais a code value of 0, and the receiver knows that the GPS satellite 15 a(15 b to 15 d) is functioning correctly.

The GPS wristwatch 10 can therefore determine if the navigation messagefrom the GPS satellite 15 a (15 b to 15 d) can be trusted.

If in step ST20 the satellite health information 72 a in FIG. 7indicates a problem with the GPS satellite 15 a (15 b to 15 d), controlgoes to step ST21.

In step ST21, the stop reception determination program 57 in FIG. 5pauses reception by the receiver device 40. Thechange-received-satellite program 59 in FIG. 5 then stores thechange-received-satellite synchronization information 74 a in thechange-received-satellite synchronization information storage unit 74 inFIG. 7 to change the GPS satellite 15 a (15 b to 15 d) from whichsignals are received.

Control then returns to step ST13, and reception of signals from anotherGPS satellite 15 a (15 b to 15 d) starts based on thischange-received-satellite synchronization information 74 a.

As a result, if there is a problem with the GPS satellite 15 a (15 b to15 d), the GPS wristwatch 10 can receive the navigation message from adifferent GPS satellite 15 a (15 b to 15 d) from which the signals canbe received normally, and the time can be reliably corrected with highprecision.

If in step ST20 the satellite health information 72 a indicates that theGPS satellite 15 a (15 b to 15 d) is functioning normally, control goesto step ST22.

Whether there is a match with the internal time information isdetermined in step ST22. More specifically, the threshold offsetdetermination program 503 in FIG. 5 determines if the offset between theinternal time data 73 b in FIG. 7, which is the current time, and thefirst reception time data 73 a 1 of the reception time data 73 a isequal to the match verification threshold value 62 a (an example of athreshold value offset) of the match verification threshold valuestorage unit 62 in FIG. 6. The match verification threshold value 62 ais approximately 0.5 second per day in this embodiment of the invention.

If a match is not confirmed in step ST22, control goes to step ST23.

The internal time data 73 b in FIG. 7 depends upon the performance ofthe real-time clock 38 that generates the internal time data 73 b. Theinternal time data 73 b is affected by the frequency shift (alsoreferred to below as the frequency shift of the real-time clock 38) ofthe crystal oscillator connected to the control unit 20 that providesthe reference clock of the real-time clock 38.

Therefore, if for some reason the frequency shift of the real-time clock38 increases and the offset between the internal time data 73 b and thefirst reception time data 73 a 1 in FIG. 7 becomes greater than thematch verification threshold value 62 a in FIG. 6, the data does notmatch and control goes to step ST23.

In step ST23 the time data acquisition program 53 in FIG. 5 gets the Zcount data from subframe 2 and subframe 3, which are the next subframesreceived from the GPS satellite 15 a (15 b to 15 d) after the Z countdata from subframe 1 is acquired. The Z count data from subframe 2 andthe Z count data from subframe 3 are then stored to the second receptiontime data 73 a 2 (an example of correction time information) and thirdreception time data 73 a 3 (an example of correction time information),respectively, of the reception time data 73 a in the time data storageunit 73 in FIG. 7. Note that the time information matching program 501in FIG. 5 described above of the GPS wristwatch 10 runs a parity checkto determine if the acquired Z count data is correct.

Step ST24 then selects the Z count data for which two or more matcheswere confirmed from among the Z count data acquired from subframe 1,subframe 2, and subframe 3. That is, the reception time matching program505 in FIG. 5 compares the first reception time data 73 a 1, the secondreception time data 73 a 2, and the third reception time data 73 a 3constituting the reception time data 73 a in the time data storage unit73 in FIG. 7.

If the difference between the data (Z count data) is substantially equalto the expected offset between the subframe data, the data is determinedto match, and the reception time data 73 a for which the match wasconfirmed is used. More specifically, the subframe data is transmittedin 6-second units, and the Z count data therefore normally differs by 6seconds from one subframe to the next.

The reception time matching program 505 therefore determines if thedifference between the first reception time data 73 a 1 and the secondreception time data 73 a 2 is 6 seconds, if the difference between thesecond reception time data 73 a 2 and the third reception time data 73 a3 is 6 seconds, and if the difference between the first reception timedata 73 a 1 and the third reception time data 73 a 3 is 12 seconds.

Control then goes to step ST25. Step ST23 therefore does not determineif the reception time data 73 a and the internal time data 73 b match.

If a match is confirmed in step ST22, control goes to step ST25. In stepST25 the stop reception determination program 57 in FIG. 5 stops thereception operation of the receiver device 40, and ends receiving thenavigation message from the GPS satellite 15 a (15 b to 15 d).

Control then goes to step ST26 where the time information adjustmentprogram 502 in FIG. 5 adjusts the internal time data 73 b in FIG. 7based on the reception time data 73 a.

When the reception time data 73 a matches the internal time data 73 b instep ST22, the first reception time data 73 a 1 of the reception timedata 73 a is used. If a match with the internal time data 73 b is notconfirmed in step ST22, the reception time data 73 a that was used isused in step ST24 is used.

The time information adjustment program 502 in FIG. 5 saves thecorrected time as the time data for timepiece display 73 c in FIG. 7.

The adjust display time data program 504 in FIG. 5 then corrects thetime displayed by the display 14 and the hands 13 on the dial 12 of theGPS wristwatch 10 based on the time data for timepiece display 73 c inFIG. 7.

The GPS wristwatch 10 thus corrects the time as described above.

FIG. 12 is a timing chart describing the reception period when thereceiver device 40 of the GPS wristwatch 10 receives a navigationmessage from the GPS satellite 15 a (15 b to 15 d). As shown in FIG. 12,when a receive command is asserted at time (A), the user operates theexternal operating unit 5 and inputs a command to receive the navigationmessage from the GPS satellite 15 a (15 b to 15 d). The GPS wristwatch10 then drives the display 14 to notify the user that receiving thenavigation message from a GPS satellite 15 a (15 b to 15 d) will begin.

The receiver device 40 does not immediately start receiving thenavigation message from the GPS satellite 15 a (15 b to 15 d) at thistime (specifically, word 10 in subframe 2) because the current time doesnot equal the preset time for starting reception (that is, 2 to 10seconds before the 0 or 30 second of the minute).

The receiver device 40 therefore enters a standby mode until the presettiming for starting reception arrives. When the preset timing forstarting reception arrives, the receiver device 40 starts receiving thenavigation message from a GPS satellite 15 a (15 b to 15 d). Thereceiver device 40 therefore does not execute the reception operationduring this standby period. As a result, the GPS wristwatch 10 cansuppress an increase in power consumption when adjusting the time.

Line (a) in FIG. 12 shows the reception pattern when a match with theinternal time data 73 b is confirmed in step ST22. Line (b) in FIG. 12shows the reception pattern when a match with the internal time data 73b is not confirmed in step ST22.

As shown in FIG. 12 (a), the receiver device 40 starts receptionapproximately 2 seconds (3 words) before subframe 1, and continuesreceiving from the TLM word to word 3 of subframe 1.

The receiver device 40 synchronizes with the C/A code of the GPSsatellite 15 a (15 b to 15 d) as a result of the satellite search. Thereceiver device 40 is therefore synchronized with the beginning of theTLM word in subframe 1 when reception starts, and can acquire the Zcount data (TOW) from the HOW word following the TLM word, and thesatellite health information from word 3.

The GPS wristwatch 10 thus shortens the reception time compared withwhen all words in subframe 1 are received. The GPS wristwatch 10 canalso know the operating condition of the satellite from the satellitehealth information acquired from word 3 of subframe 1. The GPSwristwatch 10 can therefore accurately adjust the time after a shortreception period.

In the case shown in (b) in FIG. 12, the receiver device 40 receivesfrom the TLM word to word 3 of subframe 1, and then receives the TLM andHOW words in the following subframe 2 and subframe 3. Note that thereceiver device 40 also receives the TLM word containing the preambledata in both subframes in order to synchronize reception of subframe 2and subframe 3.

As shown in FIG. 12 (b), the GPS wristwatch 10 initiates a receptionpause in which reception is temporarily stopped starting 1.8 seconds (3words) after starting to receive the TLM word in subframe 1. The GPSwristwatch 10 therefore reduces the amount of power supplied to thereceiver device 40 during this reception pause and stops reception forthe approximately 4.2 seconds of the remaining 7 words in subframe 1.

The GPS wristwatch 10 resumes reception after the reception pause ends,therefore increases the power supply to the receiver device 40, andacquires the TLM word and Z count data of the HOW word in subframe 2.

The GPS wristwatch 10 initiates another reception pause starting 1.2seconds (2 words) after starting to receive the TLM word in subframe 2,reduces the power supplied to the receiver device 40 and stops receptionfor the approximately 4.8 seconds of the remaining 8 words in subframe2.

The GPS wristwatch 10 again resumes reception after the reception pauseends, therefore increases the power supply to the receiver device 40,and acquires the TLM word and Z count data of the HOW word in subframe3.

The GPS wristwatch 10 then ends reception 1.2 seconds (2 words) afterstarting to receive the TLM word from subframe 3.

By thus providing a reception pause in which reception is stoppedtemporarily when receiving the subframe data, the GPS wristwatch 10shortens the actual reception time and receives signals efficiently. TheGPS wristwatch 10 can therefore suppress the increase in powerconsumption when adjusting the time. The reception pause period is setappropriately by the stop reception determination program 57 and thestart-reception data configuration program 58 in FIG. 5.

Note also that to allow for error in the real-time clock 38, forexample, the timing when subframe data reception starts is set slightlyearlier than the expected timing, and the timing when subframe datareception ends is set slightly later than the expected timing.

As described above, the GPS wristwatch 10 generates the receptioninstruction data 75 a when the user operates the external operating unit5 to apply a reception command to the receiver device 40, and based onthe reception instruction data 75 a the start-reception dataconfiguration program 58 tells the receiver device 40 to start receivingand acquire the Z count data from subframe 1. This enables the GPSwristwatch 10 to adjust the time (correct the internal time data 73 b)at a timing near when the user wants to adjust the time.

The GPS wristwatch 10 adjusts the time based on the reception time data73 a, which is the received satellite time information 71 a determinedby the time information matching program 501 to be correct, and cantherefore adjust the time accurately.

The start-reception data configuration program 58 of the GPS wristwatch10 tells the receiver device 40 when to receive the satellite signal inorder to correct the internal time data 73 b at a specific time based onthe internal time data 73 b. Based on the start reception data 76 a, thereception timing determination program 51 of the GPS wristwatch 10 thendetermines the timing when reception starts. It is therefore easy toadjust the time kept by the GPS wristwatch 10 because the timing whenthe time is adjusted is predetermined to, for example, the timing of the0 or 30 second of the minute.

Based on the result returned by the satellite health confirmationprogram 56, the change received satellite program 59 causes the receiverdevice 40 of the GPS wristwatch 10 to receive the navigation messagefrom a different GPS satellite 15 a (15 b to 15 d) than the GPSsatellite 15 a (15 b to 15 d) from which signals are currently beingreceived.

This enables the GPS wristwatch 10 to adjust the internal time data 73 bbased on the Z count data in a navigation message from a healthy GPSsatellite 15 a (15 b to 15 d). The GPS wristwatch 10 can thereforereliably and accurately adjust the time.

If the first reception time data 73 a 1 is determined to be unreliablewhen correcting the internal time data 73 b, the GPS wristwatch 10 canuse the second reception time data 73 a 2 or third reception time data73 a 3 to adjust the time, and can therefore prevent the internal timedata 73 b from deviating even more from the correct time.

Embodiment 2

A GPS wristwatch 10 a according to a second embodiment of the inventionis substantially identical to the first embodiment described above, likeparts are therefore identified by the same reference numerals and thefollowing description focuses on the differences between theembodiments.

More specifically, the GPS wristwatch 10 a according to this embodimentof the invention has the same configuration as the first embodimentdescribed above and shown in FIG. 1 to FIG. 4 and FIG. 6.

FIG. 15 and FIG. 16 are flow charts describing the main steps in theoperation of the GPS wristwatch 10 a according to this second embodimentof the invention. FIG. 13 shows the programs stored in the programstorage unit 150 of the GPS wristwatch 10 a, and FIG. 14 shows the datastored in the second data storage unit 170.

FIG. 17 is a timing chart describing the reception period when thereceiver device 40 of the GPS wristwatch 10 a according to the secondembodiment of the invention receives a navigation message from the GPSsatellite 15 a (15 b to 15 d).

As shown in FIG. 17, this embodiment of the invention immediately startsthe GPS satellite 15 a (15 b to 15 d) search when a receive command isasserted from the external operating unit 5 to receive the satellitesignal.

The Z count data and subframe ID are acquired from the subframe datathat is received first (see FIG. 10B). As described above, the subframeID is information identifying the subframe from which the subframe datawas received.

In this example, as shown in FIG. 17, the GPS wristwatch 10 a knows fromthe subframe ID that the first received subframe data was from subframe3. Because each subframe contains 10 words and each word is 0.6 secondlong, the GPS wristwatch 10 a knows the timing when the Z count datafrom the next subframe 1 is transmitted once the subframe ID of thereceived subframe is known.

The GPS wristwatch 10 a initiates a reception pause starting 1.2 seconds(2 words) after starting to receive the TLM word in subframe 3. The GPSwristwatch 10 a therefore reduces the amount of power supplied to thereceiver device 40 during this reception pause and stops reception forthe approximately 16.8 seconds of the remaining 8 words in subframe 3,and all of subframe 4 and subframe 5.

The GPS wristwatch 10 a then resumes reception after the reception pauseends, therefore increases the power supply to the receiver device 40,and acquires the TLM word, the Z count data of the HOW word, and thesatellite health information in word 3 of the following subframe 1. TheGPS wristwatch 10 a then ends reception 1.8 seconds (3 words) afterstarting to receive the TLM word from subframe 1.

This method enables the GPS wristwatch 10 a to receive the Z count datatwice, and thereby adjust the time more accurately.

The operation of the GPS wristwatch 10 a is described next withreference to FIG. 13 and FIG. 14 and the flow charts in FIG. 15 and FIG.16.

Differing from the first embodiment, the GPS wristwatch 10 a in thissecond embodiment of the invention starts signal reception from the GPSsatellite 15 a (15 b to 15 d) after step ST10, and executes steps(ST200, ST201) to capture a GPS satellite.

More specifically, as shown in FIG. 15, after the external operatingunit 5 is operated, a reception command is asserted, and the receptioninstruction data 75 a (command data) is stored in step ST10, the startsatellite signal reception program 508 in FIG. 13 initiates signalreception from a GPS satellite 15 a (15 b to 15 d) at the timing storedby the reception instruction data 75 a (an example of immediate timing).Control then goes to step ST201 where the satellite search program 52 inFIG. 13 outputs GPS satellite 15 a (15 b to 15 d) synchronization data,starts a GPS satellite 15 a (15 b to 15 d) search, and captures a GPSsatellite 15 a (15 b to 15 d). Control then goes to steps ST15 to ST18,which are the same as described in the first embodiment and furtherdescription thereof is thus omitted here.

If step ST18 determines the Z count data was acquired, control goes tostep ST202. In step ST202 the subframe ID confirmation program 506 inFIG. 13 acquires and stores the subframe ID following the Z count dataas the subframe ID data 77 a in FIG. 14 to the subframe ID storage unit77. This enables knowing as described above that the acquired subframedata was from subframe 3.

If the Z count data cannot be acquired in step ST18, control returns tostep ST201, but control could go to step ST202 to acquire the subframeID.

Control then goes to step ST203. In step ST203 the reception timingsetting program 507 in FIG. 13 (an example of a reception timingconfiguration unit) sets the timing for starting to receive the nextsubframe 1 based on the subframe ID data 77 a, and stores the subframe 1reception starting data 716 a in the subframe 1 reception starting datastorage unit 716.

In other words, if the subframe data was received from subframe 3, thetiming when receiving the TLM word in the next subframe 1 starts is setto a time approximately 18.0 seconds (30 words) after receiving the TLMword in subframe 3 starts.

Reception pauses until this reception start time arrives.

Control then goes to step ST204. In step ST204 the reception startingprogram 511 determines if the internal time data 73 b in FIG. 14 equalsthe subframe 1 reception starting data 716 a.

If the internal time data 73 b equals the subframe 1 reception startingdata 716 a, control goes to step ST205 and the time data acquisitionprogram 53 and other satellite information acquisition program 55 inFIG. 13 acquire the subframe 1 Z count data and satellite healthinformation.

Control then goes to step ST20. Steps ST20 to ST26 are the same asdescribed in the first embodiment, and further description thereof isthus omitted here.

However, if the internal time data 73 b in FIG. 14 has not reached thesubframe 1 reception starting data 716 a, operation pauses until theinternal time data 73 b in FIG. 14 equals the subframe 1 receptionstarting data 716 a.

The GPS wristwatch 10 a of this second embodiment of the invention canthus adjust the time more accurately because the Z count data isacquired twice.

The GPS wristwatch 10 a can thus adjust the time more efficiently undercircumstances such as described below.

If the time passed since the last time satellite signal receptionsucceeded is long and the internal time data 73 b deviates greatly fromthe actual current time, the GPS wristwatch 10 a could miss thereception timing for subframe 1.

In such cases the GPS wristwatch 10 a immediately starts the receptionoperation when a command is applied from the external operating unit 5,synchronizes with the navigation message of the GPS satellite 15 a (15 bto 15 d), acquires the subframe ID, acquires the Z count data fromsubframe 1, for example, and adjusts the time.

Because the precision of the real-time clock 38 that generates theinternal time data 73 b of the GPS wristwatch 10 a is ±15 seconds/month,the time should be adjusted as described above if the signal has notbeen received for one month or more.

Embodiment 3

A GPS wristwatch 10 b according to a third embodiment of the inventionis substantially identical to the first embodiment described above, likeparts are therefore identified by the same reference numerals and thefollowing description focuses on the differences between theembodiments.

More specifically, the GPS wristwatch 10 b according to this embodimentof the invention has the same configuration as the first embodiment asdescribed above and shown in FIG. 1 to FIG. 4.

FIG. 18 is a flow chart describing the main steps in the operation ofthe GPS wristwatch 10 b.

When the time passed from when the previous navigation message wasreceived and the satellite health information was acquired to thecurrent time is greater than or equal to a predetermined time threshold,the GPS wristwatch 10 b receives subframe 1 and acquires the Z countdata and satellite health information.

If this elapsed time is less than the predetermined time threshold, theGPS wristwatch 10 b receives the subframe data and acquires the Z countdata regardless of the subframe ID number.

The GPS wristwatch 10 b therefore receives subframe 1 if the time passedfrom when the previous satellite health information was acquired to thepresent is greater than or equal to a predetermined time, and canconfirm the operating condition of the GPS satellite 15 a (15 b to 15 d)from the satellite health information. The GPS wristwatch 10 b cantherefore determine the reliability of the acquired Z count data andaccurately correct the time.

If the time passed is less than the predetermined time, the GPSwristwatch 10 b receives the closest subframe data and acquires the Zcount data regardless of the subframe ID number, thereby shortening thereception time and adjusting the time quickly. The GPS wristwatch 10 bcan thereby suppress the increase in power consumption when adjustingthe time.

The operation of the GPS wristwatch 10 b is described next withreference to the flow chart in FIG. 18 and focusing on the differenceswith the first embodiment.

When the external operating unit 5 is operated and a receive command isasserted in step ST10, control goes to step ST300.

In step ST300, the validity of the stored satellite health informationis determined. More particularly, the satellite health confirmationprogram 56 in FIG. 5 determines if the time from when the previoussatellite health information was acquired and stored in the satellitehealth information storage unit 72 as the satellite health information72 a in FIG. 7 to the present time is greater than or equal to apredetermined time. This predetermined time is preferably approximately24 hours if the accuracy of the GPS wristwatch 10 b is ±15 seconds/monthwhen the satellite signal is not received.

If the stored satellite health information is valid in step ST300,control goes to step ST13 and GPS satellite 15 a (15 b to 15 d) signalreception starts. Operation in steps ST14 to ST18 and ST22 is the sameas described above in the first embodiment, and further descriptionthereof is omitted here.

If the stored satellite health information is not valid in step ST300,control goes to step ST11 and operation continues therefrom as describedin the first embodiment.

If the acquired Z count data matches the internal time data 73 b in FIG.7 in step ST22, control goes to step ST25 and operation continues asdescribed in the first embodiment. If the acquired Z count data does notmatch the internal time data 73 b in FIG. 7 in step ST22, control goesto step ST301.

In step ST301 the subframe data in the two subframes following thesubframe containing the Z count data acquired in step ST18 is received,and the Z count data is acquired from each of these two subframes.

Control then goes to step ST302. Step ST302 determines if there are twoor more matches with the Z counts acquired in step ST18 and step ST301.This match is decided in the same way as in step ST24 in the firstembodiment, and further description is therefore omitted here.

If two or more matches with the Z counts are confirmed in step ST302,control goes to step ST25 and operation continues as described in thefirst embodiment.

If two or more matches with the Z counts are not confirmed in stepST302, control returns to step ST13 and the above operation repeats.

The GPS wristwatch 10 b according to the third embodiment of theinvention thus accurately and quickly adjusts the time by appropriatelyselecting the subframe data to be received based on whether the timepassed from when the previous satellite health information was receivedto the present time is greater than or equal to a predetermined time. Inaddition, because the GPS wristwatch 10 b can adjust the time in a shorttime, the increase in power consumption when adjusting the time can besuppressed.

The invention is described above using a GPS satellite as an example ofa positioning information satellite, but the positioning informationsatellite is not limited to a GPS satellite and the invention can beused with Global Navigation Satellite Systems (GNSS) such as Galileo andGLONASS, and other positioning information satellites that transmitsatellite signals containing time information, including the SBAS andother geostationary or quasi-zenith satellite.

The foregoing embodiments are also described as determining in step ST10whether a command was asserted by the external operating unit 5, but theinvention is not so limited. Instead of using the external operatingunit 5 in step ST10, for example, a tilt switch or gyrosensor can bebuilt in to the GPS wristwatch, and whether a receive command has beenasserted can be determined by sensing the amount of incline or the speedof the incline of the GPS wristwatch.

The invention being thus described, it will be obvious that it may bevaried in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A time adjustment device comprising: a timeinformation generating unit that generates time information containinginternal time data and that outputs the generated time information; areception unit that receives satellite signals transmitted sequentiallyfrom a positioning information satellite in subframes that comprisesubframes 1 to 5 and that contain satellite-time-related information; anexternal input unit that generates, through manual operation of anexternal operating unit, command information that instructs thereception unit to enter a reception mode; a reception timing start setupunit that, when in the reception mode, sets the start time of receptionby the reception unit so that at least one subframe is acquired at thetime determined by the internal time data; and a corrected timeinformation storage unit that stores the satellite-time-relatedinformation; wherein the reception unit comprises a determination unitthat determines whether the satellite-time-related information receivedin a particular segment of one or more subframes is correct orerroneous, and if correct, is used as time adjustment information,wherein the generated time information is corrected based on the timeadjustment information, if a correction amount is less than or equal toa prescribed threshold amount, and wherein, if the correction amountexceeds threshold amount, then the satellite-time-related informationreceived in a subsequent subframe is stored, and if consistent, thegenerated time information is corrected based on thesatellite-time-related information.
 2. The time adjustment devicedescribed in claim 1, wherein the positioning information satellite is aGPS satellite.
 3. The time adjustment device described in claim 1,wherein a week number is contained in subframe 1, and the reception unitreceives the week number.
 4. A time adjustment device comprising: a timeinformation generating unit that generates time information containinginternal time data and that outputs the generated time information; areception unit that receives satellite signals transmitted sequentiallyfrom a positioning information satellite in subframes that comprisesubframes 1 to 5 and that contain satellite-time-related information; anexternal input unit that generates, through manual operation of anexternal operating unit, command information that instructs thereception unit to enter a reception mode; a reception timing start setupunit that, when in the reception mode, sets the start time of receptionby the reception unit so that at least one subframe is acquired at thetime determined by the internal time data; and a corrected timeinformation storage unit that stores the satellite-time-relatedinformation; wherein the reception unit comprises a determination unitthat determines whether the satellite-time-related information receivedin a particular segment of one or more subframes is correct orerroneous, and if correct, is used as time adjustment information,wherein the generated time information is corrected based on the timeadjustment information, if a correction amount is less than or equal toa prescribed threshold amount, wherein, if the correction amount exceedsthe prescribed threshold amount, then the satellite-time-relatedinformation received in each of a plurality of subsequent subframes isstored by unit as satellite time data, one out of at least two of thesatellite time data in which the difference approximately matches thedifference between the corresponding subframes is selected, and thegenerated time information is corrected based on the selected satellitetime data.
 5. A time adjustment device comprising: a time informationgenerating unit that generates time information containing internal timedata and that outputs the generated time information; a reception unitthat receives satellite signals transmitted sequentially from apositioning information satellite in subframes that comprise subframes 1to 5 and that contain satellite-time-related information; a correctedtime information storage unit that stores the satellite-time-relatedinformation; wherein, if a current corrected amount of time, which isthe amount of time the generated time information that is to becorrected based on the satellite-time-related information, exceeds aprescribed threshold amount, then the satellite-time-related informationreceived in a subsequent subframe is stored and if consistent, thegenerated time information is corrected based on thesatellite-time-related information.